Increase per-stage texture count to 96 for A11 SoC's and above. Report VkPhysicalDeviceLimits::maxPerStageDescriptorStorageImages as Metal limit of 8. Add MVKPhysicalDeviceMetalFeatures::maxPerStageStorageTextureCount and set to 8. Update VK_MVK_MOLTENVK_SPEC_VERSION to 29.